Currently, an implicit input to the sysroot build scripts is the entire current state of packages.debian.org. This makes it difficult to reproduce a given sysroot--running the script again at a later date will produce a different sysroot.

snapshot.debian.org is an official mirror of historical snapshots of the debian package archive. It would be possible to use the snapshot mirror to make the sysroot build process reproducible, which would be useful for embedders and other non-Chrome usages of the Chromium sysroot. In particular, Electron rebuilds Chromium's sysroot in order to add the 'libnotify' package, and we frequently run into issues where packages have been updated in Debian since the last sysroot build, and have additional dependencies.

See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=912524 for some potential issues with using snapshot.debian.org from AWS.